System Design

Question 1

TCP v. UDP

Answer 1

TCP
Transport layer – accuracy > speed
Connection-oriented – client and server must be connected before data sent
stateful protocol – can detect errors

UDP
speed > accuracy
real time service but some delays

Question 2

HTTP and HTTPS

Answer 2

defines method requests, addresses, default ports
works on top of Transport Layer Security

Question 3

TLS Handshake

Answer 3

client sends a request
servers submits a digital certificate
if certificate accepted by the client, client generates a session key to encrypt info transmitted during the session
handshake finishes, session begins

Question 4

websocket

Answer 4

unprovoked server send!
server send data to clients without receiving a request first
Messages to be passed back and forth

use case: real-time data. up-to-date info is critical

Question 5

transport layer

Answer 5

tcp – accuracy > speed
udp – speed > accuracy (video streaming)

Question 6

retries

Answer 6

fail fast - low limit and alert user
risk thundering herd
jitter to introduce randomness in reqs

Question 7

circuit breakers

Answer 7

opens when problem is detected
prevent cascading failures when shared resource goes down

Question 8

rate limiting

Answer 8

cap usage, prevent autoscaling > budget. control reqs by customer
token bucket
leaky bucket
fixed and sliding window

Question 9

queue based load leveling

Answer 9

order tasks in queue when they are concurrently requesting a service
introduces latency
good for scenarios when latency is ok and order matters

Question 10

gateway aggregation

Answer 10

put a gateway in front of backend to aggregate and then dispatch requests.
Risk point of failure.

Question 11

load balancing methods

Answer 11

round robin, least connections, consistent hashing

Question 12

load balancing industry standard

Answer 12

nginx, amazon elb

Question 13

load balancing pros

Answer 13

reliability, scalability, performance

Question 14

load balancing risks

Answer 14

bottleneck
need to share session data across backends
longer deploys

Question 15

scalable systems features

Answer 15

reliability (retries)
availability (rate limiting)
load balancing

Question 16

sql db pros

Answer 16

relational - foreign keys
SQL querying language
structured data
ACID compliant - all or nothing transactions

Question 17

sql db cons

Answer 17

hard to scale write-heavy systems
more work to define schema
harder to store unstructured data

Question 18

nosql db pros

Answer 18

good for unstructured data
key-value pairs stored in docs
good for scaling -> support heavy write and read systems

Question 19

nosql db cons

Answer 19

eventual consistency
harder to query multiple tables

Question 20

types of db sharding

Answer 20

geo sharding
range sharding (first letter)
hash sharding

Question 21

sharding pros

Answer 21

more scalable
faster queries with indexing
one shard downtime won’t affect all
reduce hardware costs

Question 22

sharding cons

Answer 22

not all data can be sharded
foreign key reltns only maintained within a single shard
table joins very expensive

Question 23

analytics

Answer 23

batch processing

Question 24

web crawling

Answer 24

batch processing

Question 25

large file uploads

Answer 25

job queue

Question 26

real-time events

Answer 26

stream processing - fast yet brittle

Question 27

generating a newsfeed

Answer 27

pub sub

Question 28

scheduled tasks

Answer 28

job queue, batch processing

Question 29

in-memory application caching

Answer 29

server maintains the cache more memory demands

Question 30

distributed in-memory caching

Answer 30

redis, memcache 3rd party server

Question 31

database cache

Answer 31

use db to cache

Question 32

file-system cache

Answer 32

cdn -- store commonly accessed files

Question 33

caching policies

Answer 33

FIFO LRU LFU TTL

Question 34

write through cache

Answer 34

updates cache and mem simultaneously. consistency > speed

Question 35

write-behind cache

Answer 35

updates mem and cache asynch speed> consistency

Question 36

Symmetric Encryption

Answer 36

Faster, less compute, less secure Same key for encryption and decryption. Used for communication post TLS handshake.

Question 37

Assymetric Encryption

Answer 37

Slower, more compute, more secure. Used to establish TLS handshake. RSA TLS

Question 38

In transit encryption

Answer 38

HTTPS, TLS

Question 39

at rest encryption

Answer 39

Encrypt dbs and hash and salt passwords

Question 40

messaging encryption

Answer 40

end-to-end encryption. Only stored on users' device

Question 41

Authentication

Answer 41

username and pw login 1FA, MFA Session or Token

Question 42

Session Authentication

Answer 42

server creates session id stores in cookie in users' browser stateful -- more complex

Question 43

Token Authentication

Answer 43

Server creates an encrypted token at login and client stores token in memory stateless - token stored in db

Question 44

JWT

Answer 44

small, secure, easy to parse, transparent (easy to tell if they've been tampered w)

Question 45

Types of Authorization

Answer 45

RBAC, ABAC - company wide ACL - granular

Question 46

Cloud architecture pros

Answer 46

Upfront affordability Pro maintenance Scalability Security

Question 47

Cloud architecture cons

Answer 47

Higher cost of ownership Loss of control vendor lock Industry specific regulations Location specific No airgapping

Question 48

Cloud Provider Offerings

Answer 48

VMs, GPUs, batch processing Containers Dbs Networking

Question 49

Terraform

Answer 49

Infrastructure as code Declare VMs, DNS records, low-layer resources in code

Question 50

Kubernetes

Answer 50

Declare upper-layer resources in code Group containers in clusters to manage and allocate resources

Question 51

Push CDN

Answer 51

engineer pushes CDN w every update

Question 52

Pull CDN

Answer 52

ass